Method for making molybdenum parts using metal injection molding

Abstract

Embodiments of a method for making molybdenum parts using metal injection molding are disclosed. In general, molybdenum powder is mixed or blended with a binder to form a feedstock, which is injection molded to form a green-state part. The green-state part is then sintered, such as by heating the part in a furnace for a predetermined period of time to effect consolidation and densification of the part. Desirably, the green-state part can be debound to remove at least a portion of the binder prior to sintering. In exemplary embodiments, sintering produces the final molybdenum article, and therefore the process does not require, but optionally may include, further processing of the sintered part, such as machining, cold-working, and/or hot-working.

1 . A method for making a molybdenum part, comprising:
 injection molding a feedstock to form an unsintered part, the feedstock comprising molybdenum powder and at least 45% by volume of a binder; and   sintering the unsintered part.   
     
     
         2 . The method of  claim 1 , wherein the feedstock comprises about 70% by volume of the binder. 
     
     
         3 . The method of  claim 1 , wherein the binder comprises a plasticizer, a strengthener, a compatibilizer for the plasticizer and strengthener, and a surfactant. 
     
     
         4 . The method of  claim 3 , wherein the binder has a composition comprising in weight percent about 45% to 55% plasticizer, about 45% to 55% strengthener, about 3% to 6% compatibilizer, and about 0.25% to 0.5% surfactant. 
     
     
         5 . The method of  claim 3 , wherein the binder comprises wax, polypropylene, styrene-butadiene, and stearic acid. 
     
     
         6 . The method of  claim 1 , wherein, prior to sintering, the unsintered part is debound by placing the part in a bath of at least one solvent. 
     
     
         7 . The method of  claim 6 , wherein the solvent comprises trichloroethylene. 
     
     
         8 . The method of  claim 7 , wherein the trichloroethylene is at a temperature of about 155° F. and the unsintered part is placed in the bath of trichloroethylene for about 30 to 90 minutes. 
     
     
         9 . The method of  claim 1 , wherein sintering comprises sintering the unsintered part to densify the part to at least about 95% of the theoretical density of molybdenum. 
     
     
         10 . The method of  claim 1 , wherein the molybdenum powder has a particle size ranging between about 0.1 micron and about 5 microns. 
     
     
         11 . The method of  claim 10 , wherein the molybdenum powder comprises a mixture of a first molybdenum powder having a particle size of about 0.1-0.5 micron and a second molybdenum powder having a particle size of about 3-5 microns. 
     
     
         12 . The method of  claim 1 , wherein sintering comprises heating the unsintered part at a peak temperature no greater than about 3000° F. 
     
     
         13 . The method of  claim 1 , wherein:
 prior to sintering, the unsintered part is debound to remove at least 40% of the binder; and   sintering comprises heating the part at about 500° F. for about 30 minutes, heating the part at about 1200° F. for about 30 minutes, heating the part at about 2450° F. for about 30 minutes, and heating the part at about 2550° F. for about 120 minutes.   
     
     
         14 . The method of  claim 1 , wherein:
 the feedstock is formed by mixing the metal powder and the binder, heating the metal powder and the binder to a temperature of about 300° F. to about 450° F. to form a paste, solidifying the paste, and fractionating the solidified paste to form a plurality of feedstock particles; and   injection molding the feedstock comprises introducing the feedstock particles into a hopper of an injection molding machine, heating the feedstock particles in the hopper to a temperature of about 300° F. to about 450° F. to form liquefied feedstock that is injected into a mold.   
     
     
         15 . The method of  claim 1 , further comprising placing the unsintered part between first and second setters, the first setter having an inner surface being generally contoured to the shape of and in contact with a first surface of the unsintered part, the second setter having an inner surface being generally contoured to the shape of and in contact with a second surface of the unsintered part, opposite the first surface, and wherein the unsintered part is sintered while positioned between the setters to minimize distortion of the unsintered part during sintering. 
     
     
         16 . The method of  claim 14 , wherein the setters are formed from the same feedstock as the unsintered part. 
     
     
         17 . The method of  claim 1  wherein, prior to sintering, the unsintered part is placed on a setter, the first setter having an inner surface being generally contoured to the shape of and in contact with a surface of the unsintered part, and the unsintered part and the setter are placed in a bath of at least one solvent to debind the part, and following debinding, another setter is placed on the debound part, which is then sintered while it is between the setters to minimize distortion of the part during sintering. 
     
     
         18 . The method of  claim 1  wherein, the unsintered part has a complex three-dimensional shape. 
     
     
         19 . A method for making a molybdenum part, comprising:
 injection molding a feedstock to form a green-state part, the feedstock comprising molybdenum powder and at least one binder;   debinding the green-state part to remove at least 40% of the binder to form a brown-state part; and   sintering the brown-state part at a peak temperature of no greater than about 3000° F.   
     
     
         20 . The method of  claim 19 , wherein the brown-state part is sintered at a peak temperature of no greater than about 2550° F. 
     
     
         21 . The method of  claim 19 , wherein:
 the green-state part is debound while supported on a setter having a surface that is generally contoured to an adjacent surface of the part contacting the setter; and   after debinding, another setter is placed on the brown-state part such that the part is sandwiched between the setters, said another setting having a surface that is generally contoured to the shape of an adjacent surface of the part contacting said another setter.   
     
     
         22 . The method of  claim 21 , wherein the setters are formed by metal injection molding a feedstock comprising molybdenum powder and a binder. 
     
     
         23 . The method of  claim 22 , wherein the setters and the unsintered part are formed from the same feedstock. 
     
     
         24 . The method of  claim 21 , wherein the setters and the unsintered part are made from different materials. 
     
     
         25 . A method for making a molybdenum part, comprising:
 injection molding a feedstock to form an unsintered part, the feedstock comprising molybdenum powder and at least one binder, wherein the molybdenum powder has a particle size ranging between about 0.1 micron and about 4 microns; and   sintering the unsintered part.   
     
     
         26 . The method of  claim 25 , wherein the molybdenum powder has a particle size ranging between about 0.1 micron and about 0.5 micron. 
     
     
         27 . A method for making a molybdenum part, comprising:
 forming a feedstock by mixing a metal powder and a binder, and heating the mixture to a temperature sufficient to cause the binder to melt, wherein the metal powder consists of molybdenum and has a particle size of no greater than about 5 microns, and the binder comprises at least 60% by volume of the feedstock;   injection molding the feedstock to form an unsintered part;   placing the unsintered part on an inner surface of a first setter, the inner surface being generally contoured to the shape of an adjacent surface of the part in contact with the inner surface, the first setter being formed from a feedstock formed from molybdenum powder and a binder;   debinding the unsintered part by placing the part and the first setter in a bath of at least one solvent;   placing a second setter on the unsintered part with an inner surface of the second setter contacting an adjacent surface of the part opposite the first setter, the inner surface of the second setter being generally contoured to the shape of the adjacent surface of the part contacting the second setter, the second setter being formed from a feedstock formed from molybdenum powder and a binder; and   sintering the unsintered part.